Add .desktop files for Cinnamon, and Mate.

The example files for Cinnamon do not contain the language translations for comment and name.  I'm not sure if there is an easy way to generate these or borrow from another operating system.  I've matched up all of the other settings as close as possible to what PCBSD is currently doing with .desktop files.  I've copied icons into /usr/local/share/pixmaps.  Set the icon paths in the .desktop files and renamed the .desktop files to 31 and so on.